Steady rests have been used for many years in connection with machining operations. They typically employ three hydraulically or pneumatically operated fingers which are adapted to concentrically support a shaft-like workpiece about its outer periphery to provide evenly distributed support for it. The steady rest serves to resist the tendency of the machine tool to throw the workpiece off center during machining by turning, grinding or the like. Exemplary steady rests are shown in U.S. Pat. Nos. 3,234,829 and 3,320,839 to Dinsmore, U.S. Pat. No. 2,547,529 to Lichtenberg, and U.S. Pat. No. 2,160,378 to Balsinger.
In the past, known steady rests have been designed only for use in contacting the outer periphery of the workpiece. Consequently, different mechanisms must be employed to support inner surfaces of the workpiece at its free end. When performing machining operations on solid bar stock it is possible to use the point of conventional dead centering devices to engage indentations in the end of the workpiece and hold it in place. With tubular workpieces, however, other techniques must be employed. The need to support the inner periphery of a tubular workpiece is especially important when a lathe is used to make a circumferential cut near the end of the workpiece. One commonly used support technique for tubular workpieces is to employ a plug to fill the open end of the tube. Unfortunately, these techniques take additional time thereby decreasing productivity, not to mention the expenditures required for procuring the different support devices.
The conventional steady rest assembly employs a hydraulic or pneumatic cylinder connected to the fingers. The cylinder must exert heavy pressure on the fingers during machining operations to prevent the part from going off center. This requirement for a constant and large amount of cylinder pressure is difficult to achieve in an economical manner.